Part two is: another concern you have is omitted variables. Explain in the context of this example what a plausible omitted variable might be, and why this also makes you unconvinced of your friends interpretation

1.2. Suppose that your friend tells you that they believe that this is evidence that growth causes urbanization. 'I think,' they say, 'that the richer a country gets, the more people can afford to spend on leisure, and so the more they cluster in cities where it's more exciting.' You are not fully convinced, because you know that correlation doesn't necessarily imply causation. One concern you have is reverse causality. Explain, in the context of this example, why that is a concern. (3 points)